The present invention relates to an airflow damper for controlling the flow of air in a ventilation system. In particular, the present invention relates to a multi-valve damper which divides a section of an airflow duct into at least two airflow sections, with a damper blade or valve provided for controlling the airflow in each of the airflow sections in response to sensors in each section. The present invention also provides corresponding methods for controlling airflow in a ventilation system.
Air delivery and distribution systems are used for heating, ventilation, and cooling requirements in residential and commercial structures. These systems typically consist of a variety of types and sizes of airflow ducts used to direct air to or from various locations. It is desirable in such airflow systems to be able to accurately control and regulate the airflow in the ductwork. Airflow control and regulation is typically carried out by an adjustable damper or valve, which may be controlled by airflow sensors in the ductwork.
One such prior art device is the venturi valve, such as the venturi valve manufactured by Phoenix Controls Corporation of Acton, Mass. Such venturi valves utilize a duct section in the shape of a venturi. The valve utilizes a cone which rides on a shaft. The shaft is attached to a spring having a constant that is designed to maintain a constant airflow regardless of changes in static pressure in the duct. The valve is typically designed to operate in a pressure independent manner between 0.6″ and 3.0″ water column static pressure. The shaft can be modulated to vary the flow while the spring/cone slides on the shaft to maintain its pressure independence. The valve does not directly measure airflow, rather it is calibrated in the factory over numerous points and the valve is characterized to maintain a relatively accurate flow control. The valve can be modulated using either a pneumatic or electric actuator. Because of speed and reliability, pneumatic actuation is the preferred method in critical applications such as laboratories.
Another example of a prior art valve mechanism is the Pneumavalve manufactured by Tek-Air Systems Inc. of Danbury, Conn. The Pneumavalve utilizes a series of EPDM (Ethylene-Propylene-Diene Monomer) bladders that are surrounded by sheet metal and spaced approximately 1″ apart in a metal casing. A 1-10 psi control signal inflates the bladders so that they restrict airflow in a duct. This valve can be manufactured from either stainless steel or galvanized steel/aluminum depending on the application. The valve is not by itself pressure independent and must be used in conjunction with an airflow sensor in order to be pressure independent. The valve does, however, have a very linear response to a control signal making it a good valve for use in airflow control applications. The valve has virtually no moving parts and therefore good reliability over time. The valve can only operate using pneumatic controlled air. It cannot operate electronically.
A further example of a prior art damper system is a Variable Air Volume (VAV) terminal box. There are numerous manufacturers of VAV terminal boxes including but not limited to Titus of Richardson, Tex., Anemostat of Carson, Calif., Krueger of Richardson, Tex., Tuttle & Bailey of Richardson, Tex., and Price Industries of Suwanee, Ga. A VAV terminal box is simply a cylindrical section of sheet metal with a round blade on a shaft in the duct section. The blade is rotated throughout a 90 degree arc to vary the flow in a duct. The damper in and of itself is not pressure independent but a flow sensor is typically mounted on the inlet and a simple controller is used to maintain desired flow. Because the device utilizes a pitot tube flow sensor it is limited in the turndown in flow that it can handle. Blade dampers are not linear devices so accurate control of airflow is very limited. When the device is moving from fully closed to open there is initially a relatively large change in airflow versus control signal and the reverse happens when the valve is close to fully open. This type of product is relatively inexpensive and is predominately used for temperature control where speed and accuracy is not important.
Another prior art device is the blade damper. There are numerous manufacturers of blade dampers including but not limited to Titus of Richardson, Tex., Anemostat of Carson, Calif., Krueger of Richardson, Tex., Tuttle & Bailey of Richardson, Tex., and Price Industries of Suwanee, Ga. This product is simply a cylindrical section of sheet metal with a round blade on a shaft in the duct section. The blade is rotated throughout a 90 degree arc to vary the flow in a duct. The damper in and of itself is not pressure independent but a flow sensor can be mounted on the inlet and a simple controller is used to maintain desired flow. Because the device utilizes a pitot tube flow sensor it is limited in the turndown in flow that it can handle. Blade dampers are not linear devices so accurate control of airflow is very limited. When the device is moving from fully closed to open there is initially a relatively large change in airflow versus control signal and the reverse happens when the valve is close to fully open. This type product is relatively inexpensive and is predominately used for temperature control where speed and accuracy is not important.
Opposed blade and parallel blade dampers are also known in the prior art. There are numerous manufacturers of such blade dampers including but not limited to Titus of Richardson, Tex., Anemostat of Carson, Calif., Krueger of Richardson, Tex., Tuttle & Bailey of Richardson, Tex., and Price Industries of Suwanee, Ga. This product is a rectangular section of sheet metal with multiple blades mounted on shafts in the duct section. The number of blades is dependant upon the size of the duct. The blades are rotated throughout a 90 degree arc to vary the airflow in a duct. The blades are rotated either in a parallel or opposed manner. The damper in and of itself is not pressure independent but a flow sensor can be mounted on the inlet and a controller is used to maintain desired flow. If the device utilizes a pitot tube flow sensor it is limited in the turndown in flow that it can handle. Blade dampers are not linear devices so accurate control of airflow is very limited. When the device is moving from fully closed to open there is initially a relatively large change in airflow versus control signal and the reverse happens when the valve is close to fully open. Opposed blade dampers are better for control than parallel blade dampers.
The above-described prior art has numerous shortcomings. Both the VAV terminal boxes and the Pneumavalve require a secondary device such as an airflow sensor to be pressure independent. Further, the accuracy and turndown can be seriously limited which is problematic in many applications.
The venturi valve does not use any means of measuring airflow, relying instead on factory calibration and flow characterization to achieve its stated accuracy. In addition, the venturi valve is a complicated device with numerous levers, springs and a cone that must ride smoothly on a shaft for the accuracy to be maintained.
The Pneumavalve only operates on controlled pneumatic air. The product can not operate on an electric signal. In order to use the Pneumavalve, air compressors must be supplied on a project as well as an electric to pneumatic converter to convert the electronic control signal to a pneumatic signal.
Therefore, in order to overcome the aforementioned difficulties associated with the prior art, it would be advantageous to provide a device that is designed to provide efficient and reliable airflow modulation, using either electric or pneumatic control. It would also be advantageous to provide built in airflow measurement capabilities in the device. This gives the product pressure independence over a very wide airflow range. It would also be advantageous to for such a device to divide the airflow into separate airflow sections. The resulting increased airflow velocity in each of the sections allows a much greater turndown of flow than conventional products and a more laminar flow past the flow sensors for improving accuracy. Dampers in each airflow sections can be operated separately for greater modulation control. Further, it would be advantageous if the dampers in each airflow section move in the same direction creating less turbulence and therefore less noise and system effect as compared to a conventional prior art blade damper.
It would be still further advantageous to provide a design where fewer valves will cover a wider range of airflows than VAV boxes or blade dampers, making ventilation system design and product selection easier. It would be further advantageous to provide very fast response speeds for critical applications. Such a device should be very simply constructed and have a minimum of moving parts to provide for increased reliability and durability as compared to the prior art.
The present invention provides the foregoing and other advantages.